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You can write a simple shell script and use gdal_translate utility to chop the tiles. On Mac, get the GDAL build from here. On Windows,the best way to get GDAL is via the OSGeo4W installer. In the following script, you need to replace following things
XDIM and YDIM with your source jp2 X and Y dimensions
gdal_translate with the actual path on your system
...

Based on huckfinn answers, few other comments and together with my findings:
Winning format is JPEG2000 (why and which version is mentioned below Why not others)
Why not others:
JPEG
Size limitation both data size and dimensions (4GB and 65500x65500)
no (internal) pyramids possibility = bigger the image the longer it takes to display it when pan/zoom ...

For topic 2: Here is an longer investigation of JP2, because I was also interested, to use a more efficient compression. And the result IMO is: Within GDAL/QGIS (as a QgsRastrerDataProvider) you can't combine proper jpeg2000 compression and fast caching options like tile sets and block structures in a simple way.
Normally I perfer GeoTiff for Raster-DB's, ...

For topic 1. QGIS uses GDAL as an QgsRasterdataProvider. So the capabilities of reading and writing a raster format is implemented by the GDAL lib. You can find supported a format under the following link http://www.gdal.org/formats_list.html. The command gdal-config --formats gives you an overview which format stuff is build into your lib or edition. What ...

In answer to your first question I found confirmation of the default compression quality (number) on the help page entitled Compression (Environment setting) where it says (with my bolding):
If JPEG, JPEG_YCbCr, or JPEG 2000 is selected, you can also set the
compression quality to control how much loss the image will be
subjected to by the ...

Generally I'd go with ECW over JP2 as the refresh rates for the ECW are better. There is MrSID to consider, but it is expensive - possibly more than ECW provided you're appropriately licensed, but at the extreme compression level (95% to 99%) they are clearer than similar ECW.
JP2 offers open source compressors, lossless compression and 4 band support ...

It turns out its because there were .j2i files in the directory from the previous versions of the rasters. I guess these are files created by MapInfo at runtime that contain an index of sorts which is used to decompress them.
Deleting the .j2i files resolved the issue.

I don't know what causes the program to lock, but I'd guess that the jpeg2000 files use a compression not supported by the GDAL build that your OS X QGIS uses. Some .jp2 files use compression formats (MrSID, EVW or Kakadu) that are not supported by open source libraries. GDAL Raster Formats contains an overview of the different jp2 formats and what libraries ...

If you want to read the (proprietary) ECW format, you'll have to use the proprietary libraries. Using GDAL to convert them will only work if you have the proprietary ECW libraries installed and configured in GDAL. There are other applications that read ECW (e.g. Global Mapper), but I believe they all use the proprietary libraries, and most of them are also ...

I have solved this problem by using a slightly different import specification. As Alexander Neto notes in his response, there was an issue with the web mercator.
Though the files are in WGS84 format, the location I am using the images is WGS 84/UTM zone 18N. Assigning that coordinate system in import would not place them properly. By using the more ...

If you get a dialog box prompting you to build pyramids, click "No". If they are built automatically, uncheck the option to build pyramids automatically on the Raster tab in the ArcMap Options dialog box.

$ gdalinfo ESP_032436_1755_COLOR.JP2
ERROR 4: `ESP_032436_1755_COLOR.JP2' not recognized as a supported file format.
For your older QGIS 1.8.0 install, it looks like you do not have a JPEG 2000 GDAL 1.9 driver installed. I could not get the noted .JP2 file to load at all in QGIS 1.8.0 with GDAL 1.9, but you may try by downloading and installing the ECW ...

I know that this response is 6 months late, but you could use the development build found here - http://www.gisinternals.com/sdk/ or you could build your own. In order to accomplish what you are wanting to do without obtaining a third party encoding sdk, you will need the OpenJPEG library (v2) library - http://www.gdal.org/frmt_jp2openjpeg.html